#include<iostream>
using namespace std;
class Square;
class Rectangle{
	int width,height;
	public:
		int area()
		{return (width*height);}
		void convert (Square a);
};
class Square{
	friend class Rectangle;
	private:
		int side;
	public:
		Square (int a) : side(a){}
};
void Rectangle::convert (Square a){
	width = a.side;
	height = a.side;
} 
int main(){
	Rectangle rect;
	Square sqr(4);
	rect.convert(sqr);
	cout<<rect.area();
	return 0;
}